A multi-function torque converter with an impeller clutch to substantially non-rotatably connect an impeller to a cover for the torque converter, and a torque converter clutch to connect a turbine to the cover is known. It is know to use three controllable fluid circuits (three-pass) to provide pressurized fluid to and to drain fluid from the torus and two pressure chambers to control operation of the impeller and torque converter clutches. A pump in a transmission is typically used to provide pressurized fluid for the torque converter and to drain fluid from the torque converter. However, most known transmissions can only provide two controllable fluid circuits making the three-pass design unusable with these transmissions.
For a multi-function torque converter with only two controllable fluid circuits (two-pass), it is known to close the impeller clutch and then to close the torque converter clutch in series. For example, to use the same fluid circuit to provide apply pressure to close both the impeller clutch and the torque converter clutch. However, this process reduces the pressure bandwidth for both clutches. Further, the torque converter clutch apply pressure for known multi-function torque converters typically starts at a higher level than in a conventional torque converter. As a result, there is need for higher pressure in the circuit and increased pump capacity, and efficiency of the hydraulic system decreases. In addition, with a two-pass design it is difficult to control the closing of the impeller clutch, for example, the impeller clutch typically closes too abruptly causing an uncomfortable sensation for the driver of the vehicle including the torque converter.
FIG. 11 is a partial cross-sectional view of prior art torque converter 300 with turbine clutch 302. Torque converter 300 includes cover 304, impeller 306 with impeller shell 308, and turbine 310 including turbine shell 312. Clutch 302 acts as a lock-up clutch for converter 300. For example, for torque converter mode, pressure in torus 314, formed by impeller 306 and turbine 308, is greater than pressure in chamber 316 at least partially formed by cover 304 and turbine shell 312, and clutch 302 is open. Torque flows from the cover to output hub 318 via impeller 306, the turbine 310, and torsional damper 320.
In lock-up mode, pressure in chamber 316 is greater than pressure in torus 314, closing clutch 302 and non-rotatably connecting impeller shell 308 and turbine 310. Torque flows from cover 304 to hub 318 via shell 308, shell 312, and damper 320.
In lock-up mode, high pressure in chamber 316 is needed to close clutch 302. This pressure results in force F1 in direction D on portions 312A and 308A of turbine shell 312 and impeller shell 308, respectively. Portion 308B of shell 308 is relatively thick and buttressed by blades 322 for the impeller. Portion 308A is relatively flexible compared to portion 308B. Therefore, in response to force F1, portion 308B remains stable and portion 308A flexes in direction D. As a result of the flexing of portion 308A, stress and strain is placed on corner 308C of shell 308 decreasing the service life of shell 308 and increasing the likelihood of failure of shell 308.